Fuel cells are devices that directly convert chemical energy of reactants, i.e., fuel and oxidant, into direct current (DC) electricity. For an increasing number of applications, fuel cells are more efficient than conventional power generation, such as combustion of fossil fuel, as well as portable power storage, such as lithium-ion batteries.
In general, fuel cell technology includes a variety of different fuel cells, such as alkali fuel cells, polymer electrolyte fuel cells, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells and enzyme fuel cells. Today's more important fuel cells can be divided into several general categories, namely (i) proton exchange membrane or polymer electrolyte membrane (PEM) fuel cells that use compressed hydrogen (H2) as fuel or substances that can be reformed into hydrogen, such as alcohols, e.g., methanol (CH3OH), metal hydrides, e.g., sodium borohydride (NaBH4), hydrocarbons, or other reformable fuels; (ii) PEM fuel cells that can consume non-hydrogen fuel directly or direct oxidation fuel cells, such as direct methanol fuel cells (DMFC); and (iii) solid oxide fuel cells (SOFC) that directly convert hydrocarbon fuels to electricity at high temperature.
Most hydrogen fuel cells have a proton exchange membrane or polymer electrolyte membrane (PEM), which allows the hydrogen's protons to pass through but forces the electrons to pass through an external circuit, which advantageously can be a cell phone, a personal digital assistant (PDA), a computer, a power tool or any device that uses electron flow or electrical current. The fuel cell reaction can be represented as follows:
Half-reaction at the anode of the fuel cell:H2→2H++2e−
Half-reaction at the cathode of the fuel cell:2(2H++2e−)+O2→2H2O
Generally, the PEM is made from a polymer, such as Nafion® available from DuPont, which is a perfluorinated sulfonic acid polymer having a thickness in the range of about 0.05 mm to about 0.50 mm, or other suitable membranes. The anode is typically made from a Teflonized carbon paper support with a thin layer of catalyst, such as platinum-ruthenium, deposited thereon. The cathode is typically a gas diffusion electrode in which platinum particles are bonded to one side of the membrane.
For DMFC, the chemical-electrical reaction at each electrode and the overall reaction for a direct methanol fuel cell are described as follows:
Half-reaction at the anode:CH3OH+H2O→CO2+6H++6e−
Half-reaction at the cathode:1.5O2+6H++6e−→3H2O
The overall fuel cell reaction:CH3OH+1.5O2→CO2+2H2ODMFCs are discussed in U.S. Pat. Nos. 4,390,603 and 4,828,941, which are incorporated by reference herein in their entireties.
In a chemical metal hydride fuel cell, sodium borohydride is reformed and reacts as follows:NaBH4+2H2O→(heat and/or catalyst)→4(H2)+(NaBO2)Suitable catalysts for this reaction include platinum and ruthenium, and other metals. The hydrogen fuel produced from reforming sodium borohydride is reacted in the fuel cell with an oxidant, such as O2, to create electricity (or a flow of electrons) and water by-product, illustrated above. Sodium borate (NaBO2) by-product is also produced by the reforming process. A sodium borohydride fuel cell is discussed in U.S. Pat. No. 4,261,956, which is incorporated by reference herein in its entirety.
Valves are needed for regulating and transporting fuel between fuel cartridges, fuel cells and/or fuel refilling devices. The known art discloses various valves and flow control devices, such as those described in U.S. Pat. Nos. 6,506,513 and 5,723,229 and in U.S. published Application Nos. 2003/0082427 and 2002/0197522. A need, however, exists for improved valves that allow venting of gas, maintaining seals, and improving the flow of fuel through the valve, among other things. To a certain extent, this need has been addressed by commonly owned, co-pending U.S. Published Application Nos. 2005/0022883 and 2006/0196562, as well as U.S. patent application Ser. No. 10/978,949, which are incorporated herein by reference in their entireties. Nonetheless, there still exists the need for a check valve that can automatically open and close in response to pressure and still positively seal against back flow.